The present invention relates generally to magnetic tape recording/playback equipment, and in particular, to an apparatus for detecting splices in such tapes.
Many applications involving the use of magnetic recording tapes give rise to the need to attach or splice respective portions of tape together. In using such tapes to record and play back material, it is generally desirable to avoid placing recorded materials over the splice since irrespective of the quality of the splice, it is not uncommon for discontinuities or drop-outs in the recorded material to occur as the splice passes the magnetic heads of the recording/playback equipment as a result of the discontinuity at the tape surface where the splice has been made.
Although such drop-outs can be extremely annoying in connection with any of a number of magnetic recording applications, this problem is of particular importance in connection with endless loop magnetic recording tape cartridges of the type which are currently in prevalent use in broadcast applications. Such cartridges make use of an endless loop of tape wound within the cartridge so as to enable material recorded on the tape to be repeatedly played in continuous fashion, without the need to rewind the tape. While such tapes are extremely useful in broadcast applications, the structure of the cartridge of necessity requires that at least one tape splice be provided in each cartridge, to develop the endless loop. Moreover, since such cartridges are being used in broadcast applications, the reproduction of drop-outs is unacceptable.
Recognizing this, recordings made using endless loop tape cartridges are preferably initiated just after the tape splice has passed the recording head to maximize the amount of tape which is available to receive the recording before the tape splice is again encountered. While location of the tape splice may be accomplished visually, this is rather difficult and is not acceptable for broadcast applications. Accordingly, the need has arisen to develop a means for automatically detecting the tape splice to "set up" the cartridge for optimized use. Conceptually, this involves equipment which is capable of automatically detecting passage of a tape splice, and stopping transport of the tape at an appropriate time after the splice has been detected so as to make sure that the splice will be located beyond the heads of the recording/playback unit.
One method which has been used to accomplish this is to record a signal on a track of the magnetic recording tape, making sure the recorded signal traverses the splice, and to detect the resulting drop-out as the recorded signal is played back. However, this method is susceptible to error when the splice produced is good in quality, or the test recording is relatively noisy in relation to the quality of the splice.
Another method which has been used to accomplish this result is to optically sense passage of the tape splice. This involves use of a splicing material which is different in color or reflectivity than the magnetic recording tape. Optical sensors are then provided which are capable of sensing passage of the splice by detecting such changes in color or reflectivity. This technique is marginally effective when the tape splice is relatively new. However, after repeated use, film from the tape and grease from the transport mechanism generally tend to discolor the splicing material, causing a deterioration if not a complete loss of the optical differences which are to be sensed, and accordingly compromising the utility of such devices.
Another method which has been used to detect the passage of a tape splice is to mechanically monitor differences in thickness of the tape, signifying passage of the tape splice. However, magnetic recording tapes are generally on the order of 1 mil in thickness, and the splicing material is generally of similar thickness to assure correct transport of the spliced tape through the cartridge. This makes the mechanical detection of a tape splice rather difficult. Generally, mechanical splice detection is accomplished by attaching a lever mechanism to the pinch roller which secures the tape to the capstan of the recording/playback unit so that changes in thickness of the tape passing between the pinch roller and the capstan will cause movement of the lever mechanism. Movement of the lever mechanism may be used to trigger some form of activation switch, such as a mechanical (micro) switch, an optical switch or a magnetic switch, or to produce a current in an associated coil using a moving magnet or the like. Examples of such efforts may be had with reference to U.S. Pat. Nos. 4,142,221 and 3,854,643.
Such efforts have also not proven to be entirely satisfactory. First, such techniques necessitate the attachment of additional and separate mechanical components to the pinch roller assembly of the tape transport mechanism. Such placement adds undesirable weight and structure to the pinch roller assembly which can adversely affect its normal operation. Second, in view of the small changes in thickness which must be detected, extreme precision in adjustment is required to assure correct operation, requiring frequent, tedious calibration procedures.
It therefore remained desirable to develop an apparatus for detecting passage of a tape splice which is reliable in operation, and which does not require the use of ancillary mechanical components requiring extensive calibration and adjustment.